The State University of New York Health Science Center at Brooklyn (SUNY/HSCB) site proposes to recruit at least 50 pregnant HIV infected women per year into the WITS. The investigators state that their site has a track record going back eleven years of identifying, recruiting and retaining such a population into longitudinal studies. This program is directed by three senior clinician researchers Dr. Sheldon H. Landesman, Howard L. Minkoff and Hermann A. Mendez who together have nearly 40 years experience in HIV cohort studies. This site, invited into the WITS in 1991 has averaged approximately 50 new study entrants a year. Retention at the second and third year time points are 91.4% and 77.4% respectively for mothers and 82% and 75% for infants. Over the course of more than 3200 visits we have had only 343 or 11% missed visits. This site has an extensive array of 21 integrated research and service programs which serve the needs of over 2,000 HIV infected patients. The extensive linkages within the community and with other hospitals allow the applicants to easily recruit from the 340 to 350 HIV infected pregnant women giving birth in the borough of Brooklyn each year. The SUNY/HSCB site has subcontracted with Dr. Jane Pitt's laboratory at Columbia Presbyterian to perform all virology, immunology and repository work. Dr. Pitt's laboratory has an outstanding record in performing WITS required assays and is ACTG certified. The applicants state that scientifically, Drs. Landesman, Mendez and Minkoff are widely published in the field of perinatal HIV disease. Dr. Landesman was first author on a recent WITS paper in New England Journal of Medicine (NEJM) on "Obstetrical Variable and HIV Transmission." He also serves on five of the eight working groups. Dr. Minkoff is the premier obstetrician on HIV Disease in women in the country. He is the WITS liaison to the WIHS study and currently chairs two committees working towards papers. The SUNY site proposes a collaboration with Dr. Stephen J. O'Brien from the Laboratory of Genetic Diversity (NCI) and Dr. Thomas R. O'Brien (Viral Epidemiology Branch, NCI) to study the role of genetic factors including, but not limited to, the CKR5 gene on transmission and disease progression.